69 lines
1.6 KiB
Python
69 lines
1.6 KiB
Python
#!/usr/bin/env python3
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"""Minimal NFQUEUE example: rewrite DNS queries from example.com to pwned.com."""
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import signal
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import sys
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from netfilterqueue import NetfilterQueue
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from scapy.all import DNS, DNSQR, IP, UDP
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SOURCE_QNAME = b"example.com."
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TARGET_QNAME = b"pwned.com."
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nfq = NetfilterQueue()
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def _handle_packet(packet) -> None:
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try:
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ip = IP(packet.get_payload())
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if ip.haslayer(UDP) and ip.haslayer(DNS) and ip.haslayer(DNSQR):
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dns = ip[DNS]
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query = ip[DNSQR]
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# Only touch DNS requests for exactly example.com.
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if dns.qr == 0 and query.qname == SOURCE_QNAME:
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query.qname = TARGET_QNAME
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# delete fields so scapy re-calculates them
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del ip.len
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del ip.chksum
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del ip[UDP].len
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del ip[UDP].chksum
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packet.set_payload(bytes(ip))
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except Exception:
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pass
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packet.accept()
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def _stop(_sig, _frame) -> None:
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raise SystemExit(0)
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def main() -> int:
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if len(sys.argv) != 2:
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print("Usage: dns_rewrite_example_to_pwned.py <qnum>", file=sys.stderr)
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return 1
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try:
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qnum = int(sys.argv[1])
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except ValueError:
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print("qnum must be an integer", file=sys.stderr)
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return 1
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signal.signal(signal.SIGINT, _stop)
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signal.signal(signal.SIGTERM, _stop)
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nfq.bind(qnum, _handle_packet)
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try:
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nfq.run()
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except KeyboardInterrupt:
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pass
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finally:
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nfq.unbind()
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return 0
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if __name__ == "__main__":
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raise SystemExit(main())
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